Enviornmental Controls I - Final Exam

Insolation

Incoming solar radiation at the surface of the Earth
1. UV: Damaging to materials and can cause health issues
2. Visible (daylight)
3. Infrared (heat)

Transmittance

ratio of total amount of transmitted light to total incident light; can be diffuse or non-diffuse

Specular Reflectance

Reflection of parallel light rays in a single, defined direction from a smooth surface; results in a clear image (ex: mirror)

Diffuse Reflectance

Scattering of light in many directions from a rough surface resulting in a blurred, scattered appearance with no distinct image; may be “matte”.

Luminous Intensity

The force that generates light and describes distribution of light; units: candela (cd)

Intensity of Light

Luminous Flux

photometric power as perceived by the human eye “total amount of lightness”; frequency dependent due to the relative sensitivity of the eye; units: lumens

Describes power and supply of light; total light emitted, quantity of lumens.

555 nm

maximum wavelength where human sensitivity is greatest; yellow-green region

Illuminance

density of luminous power/ total luminous flux incident on a surface, per unit area (related to luminous flux); inversely proportional to square of distance; units: footcandles/lux; 1 fc = 10.764 lux

Luminance

luminous intensity per unit of apparent area; units: cd/ft² or cd/m²

Brightness

subjective reaction to luminance of radiating or reflecting source

Cones and Rods

Cones = cell sensitive to color; Rods = cells responde to motion + dim light conditions

Foveal Vision

2 degree CONE @ center of vision that allows for acute detail perception 

1. Most of the information on detail and color

Near-Field Vision

binocular (wider field) vision; color vision; 60° cone; depth perception

Far-Field Vision

Peripheral vision; ~145°; motion detection; lots of rods

Horizontal Work Surface Height

the height at which to measure a task at hand; example: desk height at 30” above ground

Illuminance Levels

quantity of light falling on a surface; relates to work plane

Glare

sensation produced by luminances within the visual field that are greater than the luminance to which the eyes are adapted, which causes annoyance, discomfort or loss in visual performance → excessive luminance ratios

Direct Glare

glare resulting from high luminances (or insufficiently shielded light sources ) in the field of view

1. Usually associated with bright areas outside the visual task or region being viewed; luminaires, ceilings, windows 

2. Discomfort is due to:

   1. Eye quickly adapts to the average brightness of the overall scene

   2. Eye is attracted to the highest luminance in the scene

3. Light sources will cause more direct glare if near the center of vision, larger (greater apprehended angle), higher luminance, on dark background

Indirect Glare

Reflections that are superimposed upon diffuse reflections from an object that partially or totally obscure the details to be seen by reducing contrast.

1. Dark and specular surfaces can produce very severe glare conditions

2. Reflected glare - specular surfaces

3. Veiling reflection - dull and semi-matte surfaces with some specularity

4. Can be more difficult to control than direct glare

5. You can produce visibility by REDUCING CONTRAST 

6. Most pronounced when incident angle = viewing angle 

   1. 20 degrees to 40 degrees

   2. figure: @ 22 degrees to 27 degrees, contrast is negative -> background luminance exceeds that of the task, task is not visible

Offending Zone

The area from which a luminaire or bright object can reflect light off the task and into the viewer’s eyes

Luminance Ratio

1. Ratio between the luminances of any two areas in the visual field

   1. Luminance of the various surfaces in the normal field of vision need to be kept within acceptable limits

   2. When eye fixates on a task, an adaption level is established 

      1. As eye shifts from on luminance to another, it must adapt to new level and if the difference is great, discomfort and fatigue can be experienced

Perception of Brightness

1. Dependent on luminance, contrast and human perception

2. One can increase the perception of brightness by decreasing the overall quantity of light because you change the ratio or contrast of the overall scene; since the eyes adjust to the average luminance of the scene, if the overall average luminance decreases, the perception of light decreases.